Aluminum alloy

ABSTRACT

The present invention relates to an aluminum alloy. The present invention provides an aluminum alloy composed of, by weight, 0.2% or less of Si, 0.2% or less of Fe, 0.6% or less of Mn, 1.5-2.1% of Mg, 5.5-6.5 of Zn, 0.1% or less of Ti, 0.1% or less of Cr, 0.1% or less of Zr, inevitable impurities, and the balance Al.

TECHNICAL FIELD

The present invention relates to an aluminum alloy, and more particularly, to an aluminum alloy of high strength, which is used as a material for appearance of an electronic device.

BACKGROUND ART

Generally, various types of electronic devices are provided with materials for appearance, such as a cover case, a case frame and a bezel, in order to protect various kinds of components mounted in the electronic devices. Such a material for appearance requires a high strength in order to prevent damage of an electronic device from an impact.

As an electronic device has a complicated structure, a small size and a thin thickness, there is a limitation in implementing a material for appearance by the conventional press processing. Thus, an extruded material for appearance of an electronic device, using an extrusion method for freely implementing a shape, is being developed variously. Through the extruded material using the extrusion method, a product needs not be treated because of a precise size of the prepared product, and because of many advantages such as an excellent mechanical characteristic, a massive production, and a low production cost.

When a material for appearance of an electronic device is prepared by the extrusion method, an aluminum alloy is mainly used, and aluminum is categorized according to an alloy type. More specifically, widely used is a method for classifying an aluminum 1000 alloy as pure aluminum containing 99.00 wt % or more of aluminum, an aluminum 2000 alloy as an Al—Cu alloy, an aluminum 3000 alloy as an Al—Mn alloy, an aluminum 4000 alloy as an Al—Si alloy, an aluminum 5000 alloy as an Al—Mg alloy, an aluminum 6000 alloy as an Al—Mg—Si alloy, and an aluminum 7000 alloy as an Al—Zn—Mg alloy.

As the material for appearance, an aluminum 6000 alloy of high strength is mainly used for high rigidity and easy preparation. More specifically, an aluminum 6000 alloy of Al—Mg—Si has high strength by an age hardening effect through a control of a precipitate phase of magnesium silicide (Mg2Si). However, an appearance implementation is difficult if the amount of Mg and Si is increased for high strength, and the aluminum 6000 alloy has a lower strength than an aluminum 7000 alloy. Accordingly, efforts to apply an aluminum 7000 alloy of high strength, which is much used at an automobile and an airplane, and used as a structural material such as a construction material, to electronic devices are actively ongoing.

An aluminum 7000 alloy of Al—Zn—Mg—(Cu) has stains, streaking, black dots, or spots on its surface after an anodizing process, by a large amount of added materials and a shape of formed internal tissues. In order to obtain the strength of the aluminum 7000 alloy, copper (Cu) may be added to enhance the strength by generating an aluminum-copper alloy (Al2Cu) phase. However, the aluminum 7000 alloy having copper added thereto becomes yellowish after an anodizing process. Even if the aluminum 7000 alloy having copper added thereto has a sufficient strength, the material for appearance of an electronic device has a difficulty in implementing an aesthetic impression of high quality, due to defects on its surface and a yellow color phenomenon. Therefore, the present invention provides an aluminum alloy having a high strength and a high aesthetic impression through a control of the aluminum 7000 alloy.

DISCLOSURE Technical Problem

An object of the present invention is to provide an aluminum alloy of high strength, which is used as a material for appearance of an electronic device.

Another object of the present invention is to provide an aluminum alloy used as a material for appearance of an electronic device, capable of preventing from becoming yellowish after an anodizing process.

Another object of the present invention is to provide an aluminum alloy used as a material for appearance of an electronic device, which does not have metallic streaking and defects on its surface.

Technical Solution

According to an aspect to achieve the above purposes, the present invention provides an aluminum alloy composed of, by weight: 0.2% or less of Si; 0.2% or less of Fe; 0.6% or less of Mn; 1.5˜2.1% of Mg; 5.5˜6.5% of Zn; 0.1% or less of Ti; 0.1% or less of Cr; 0.1% or less of Zr; inevitable impurities; and the balance Al.

In an embodiment, the aluminum alloy may further comprise 0.1% or less of Cu.

In an embodiment, the alloy may be composed of equiaxed grains.

In an embodiment, an average aspect ratio of particles of the alloy may be 0.6˜1.3.

In an embodiment, an average grain size of the particles of the alloy may be 30˜500 μm.

In an embodiment, b value may be −0.5˜0.5 on 3D coordinates of Lab color system.

In an embodiment, a ratio (Zn/Mg) of a weight amount of Zn with respect to a weight amount of Mg may be 3˜4.

Advantageous Effect

The aluminum alloy used as a material for appearance according to the present invention may have its strength controlled by reducing the amount of copper (Cu), and by controlling the amount of magnesium (Mg) and zinc (Zn). This may enhance the strength of the aluminum alloy material for appearance.

Further, in the present invention, yellowing due to copper (C) after an anodizing process may be prevented by reducing the amount of copper. Accordingly, a unique color of a dye may be represented at the time of applying the dye on the aluminum alloy material for appearance, thereby significantly enhancing an aesthetic impression of the aluminum alloy.

Further, in the present invention, a metallic tissue may be controlled by controlling the amount of the alloy. Accordingly, the aluminum alloy material for appearance may be composed of equiaxed grains. As a result, the aluminum alloy material for appearance does not have a shape of a metallic tissue on its surface, and does not have surface defects such as stains and black dots. Accordingly, when a dye is painted on the aluminum alloy material for appearance, the dye may be uniformly painted without influence of surface defects. This may significantly enhance an aesthetic impression of the aluminum alloy material for appearance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an embodiment of an electronic device using an aluminum alloy material for appearance according to the present invention;

FIGS. 2A and 2B are images of tissue shapes according to comparative example 1 and preferred example 1 each having a composition ratio shown in table 1;

FIG. 3 shows images of specimens after an anodizing process, according to comparative example 2 and preferred example 2 each having a composition ratio shown in table 3; and

FIG. 4 is a flowchart for preparing an aluminum alloy material for appearance of an electronic device according to the present invention.

MODES FOR CARRYING OUT THE PREFERRED EMBODIMENTS

Description will now be given in detail according to exemplary embodiments disclosed herein, with reference to the accompanying drawings. For the sake of brief description with reference to the drawings, the same or equivalent components may be provided with the same or similar reference numbers, and description thereof will not be repeated. In the present disclosure, that which is well-known to one of ordinary skill in the relevant art has generally been omitted for the sake of brevity. The accompanying drawings are used to help easily understand various technical features and it should be understood that the embodiments presented herein are not limited by the accompanying drawings. As such, the present disclosure should be construed to extend to any alterations, equivalents and substitutes in addition to those which are particularly set out in the accompanying drawings.

It will be understood that although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are generally only used to distinguish one element from another.

A singular representation may include a plural representation unless it represents a definitely different meaning from the context.

Terms such as “include” or “has” are used herein and should be understood that they are intended to indicate an existence of several components, functions or steps, disclosed in the specification, and it is also understood that greater or fewer components, functions, or steps may likewise be utilized.

FIG. 1 is an embodiment of an electronic device using an aluminum alloy material for appearance according to the present invention.

Referring to FIG. 1, illustrated is a mobile terminal using an aluminum alloy material for appearance according to an embodiment of the present invention. The aluminum alloy material for appearance may protect inner components at an outermost region of an electronic device, such as a cover case 100 or a bezel 200 of the mobile terminal.

The cover case 100 and the bezel 200 should have the strength high enough to protect inner components of an electronic device. In this aspect, copper has been much utilized as a component of an alloy material for appearance, because it increases the strength of the alloy material for appearance. However, if copper is added to the alloy material for appearance, the alloy material for appearance may become yellowish.

More specifically, an alloy material for appearance, used at the cover case 100 and the bezel 200, should serve to represent a unique color of a dye at the time of applying the dye. If the alloy material for appearance becomes yellowish, a unique color of a dye is lowered at the time of applying the dye. Thus, if an alloy material for appearance, which does not become yellowish, is used at the cover case 100 and the bezel 200, a unique color of a dye is represented at the time of applying the dye, resulting in enhancing an aesthetic impression.

The aesthetic impression of metallic tissues of the cover case 100 and the bezel 200 may be lowered due to surface defections such as streaking, stains and black dots. More specifically, particles of the metallic tissues may be seen on the surface, due to an external pressure, etc., at the time of preparing an alloy material for appearance, thereby forming stains and black dots. If the particles of the metallic tissues are seen on the surface of the alloy material for appearance, the alloy material for appearance may have a lowered aesthetic impression at the time of applying a dye. Here, the stains and the black dots may also cause the alloy material for appearance to have a lowered aesthetic impression.

If the metallic tissues are composed of equiaxed grains (isometric crystals), the particles of the metallic tissues may be prevented from being seen on the surface of the alloy material for appearance, and occurrence of stains and streaking may be prevented.

The present invention provides an alloy material for appearance which does not become yellowish, which can prevent particles of metallic tissues from being seen on the surface of the alloy material for appearance, and which has the strength high enough to protect inner components of a mobile terminal.

For this, the alloy material for appearance according to an embodiment of the present invention may be an aluminum alloy composed of, by weight, 0.2% or less of Si, 0.2% or less of Fe, 0.6% or less of Mn, 1.5˜2.1% of Mg, 5.5˜6.5% of Zn, 0.1% or less of Ti, 0.1% or less of Cr, 0.1% or less of Zr, inevitable impurities, and the balance Al.

Hereinafter, each composition will be explained in more detail. As for Si and Fe, 0.2% or less of Si, and 0.2% or less of Fe may be used by wt per 100%. If each of Si and Fe exceeds 0.2% by wt per 100%, an intermetallic compound is formed to degrade high-temperature moldability. Therefore, it is preferable that the amount of each of Si and Fe does not exceed 0.2% by wt per 100%.

As for Mn, 0.6% or less of Mn may be used by wt per 100%. Mn forms various dispersed particles by combining with Al. As a result, grain refining is implemented, and a dispersion effect of micro precipitates is generated. Through the dispersion effect of micro precipitates, the strength of the alloy may be increased. If the amount of Mn exceeds 0.6% by wt per 100%, recrystallization of the alloy is restricted, and the strength of the alloy may be lowered. Therefore, it is preferable that the amount of Mn does not exceed 0.6% by wt per 100%.

The amount of Mg may be 1.5%˜2.1% by wt per 100%. Mg is an element added for hardening of a solid solution. If Mg is added with an amount less than 1.5%, an age hardening effect is drastically lowered to reduce the strength of the alloy. On the other hand, if Mg is added with an amount more than 2.1%, a coarse precipitate phase is generated to increase a pressure at the time of an extrusion, thereby lowering compression moldability. Therefore, it is preferable that the amount of Mg is 1.5%˜2.1% by wt per 100%.

The amount of Zn may be 5.5%˜6.5% by wt per 100%. Zn is an element added for enhancing the strength without the loss of a corrosion resistance. If Zn is added with an amount less than 5.5%, the strength of the alloy may be reduced. On the other hand, if Zn is added with an amount exceeding 6.5%, stress corrosion cracking may be degraded and compression productivity may be also lowered. Therefore, it is preferable that the amount of Zn is 5.5%˜6.5% by wt per 100%.

In an embodiment of the present invention, a ratio of a weight amount of Zn with respect to a weight amount of Mg (Zn/Mg) may be within the range of 3˜4. More specifically, when the ratio (Zn/Mg) is less than 3, the strength of the aluminum alloy may be lowered. On the other hand, when the ratio (Zn/Mg) exceeds 4, stress corrosion cracking in the alloy may be degraded. Further, in the aluminum alloy of the present invention, even if the amount of Cu to be explained later is low, a desired strength of the alloy may be obtained by controlling the ratio of the weight amount of Zn with respect to the weight amount of Mg (Zn/Mg). That is, in the present invention, an extrusion molding and a mechanical strength are significantly enhanced by controlling the amount of Mg, Zn and Cu.

The amount of Ti may be 0.1% or less by wt per 100%. Ti is an element which causes grain refining by reducing the size of a large intermetallic compound. Thus, the strength of the aluminum alloy may be enhanced by addition of Ti. If the amount of Ti exceeds 0.1% by wt per 100%, compression moldability of the alloy is lowered, and a coarse compound is generated to lower toughness. Therefore, it is preferable that the amount of Ti does not exceed 0.1% by wt per 100%.

The amount of each of Cr and Zr may be 0.1% or less by wt per 100%. Cr and Zr are elements added to prevent grain refining and a recrystallization layer, and to form a fibrous crystal by preventing a recrystallization at the time of an extrusion. If the amount of each of Cr and Zr exceeds 0.1% by wt per 100%, an unnecessary dispersed phase may be precipitated in a grain boundary, resulting in lowering the strength. Therefore, it is preferable that the amount of each of Cr and Zr does not exceed 0.1% by wt per 100%.

The amount of Cu may be 0.1% or less by wt per 100%. Cu is an element to increase the strength of the alloy by generating an Al2Cu phase in the aluminum alloy. However, if the amount of Cu exceeds 0.1% by wt per 100%, the alloy becomes yellowish after an anodizing process, thereby having a difficulty in being used as a material for appearance of an electronic device. Therefore, it is preferable that the amount of Cu does not exceed 0.1% by wt per 100%. Furthermore, the aluminum alloy according to the present invention, which has the aforementioned compositions, may have an equiaxed grain tissue having a yield strength of 350˜450 MPa.

In an embodiment, the aluminum alloy according to the present invention may be composed of equiaxed grains. As a result, particles of metallic tissues are not seen on the surface of the aluminum alloy according to the present invention, and surface defects such as black dots do not occur.

In the specification, the statement which the aluminum alloy is composed of equiaxed grains may define that an average aspect ratio of particles of the alloy is 0.6˜1.3. Here, the aspect ratio of the particles of the alloy may be calculated by analyzing an image obtained by capturing the sectional surface of the alloy, through a well-known image analysis program.

An average grain size of the particles of the alloy may be 30˜500 μm. If the average grain size of the particles is less than 30 μm, streaking may occur on the surface of the alloy. On the other hand, if the average grain size of the particles exceeds 500 μm, stains may occur on the surface of the alloy with a high probability.

The aluminum alloy according to the present invention may be prevented from becoming yellowish after an anodizing process, by controlling the amount of Cu. More specifically, the aluminum alloy according to the present invention does not become yellowish after an anodizing process. As for the color of the alloy after an anodizing process, b value may be −0.5˜0.5 on 3D coordinates of L*a*b* (Lab) color system. The L*a*b* color system will be explained in more detail in descriptions of FIG. 3.

Hereinafter, embodiments of the present invention will be explained. In order to check characteristics of the aluminum alloy according to the present invention, prepared were specimens each having composition ratios shown in the following table 1, within the scope of the present invention.

TABLE 1 Weight % Si Fe Cu Mn Mg Zn Cr Ti Zr Al Comparative example 1 0.03 0.06 0.74 0.04 1.94 5.87 0.13 0.03 0.11 Bal. (Commercial 7041) Preferred example 1 0.05 0.1 0.02 0.12 1.16 5.95 <0.05 0.03 <0.1 Bal.

In order to compare the characteristics of the comparative example 1 (commercial 7041) and the preferred example 1 each having composition ratios shown in the table 1, a tensile strength and a yield strength of each of the specimens were measured by a Universal Testing Machine (specimen size: E8/E8M Standard Specimen). Then, result values through the measurement were operated to calculate an elongation percentage. And tissue shapes of the specimens were shown in the following table 2.

TABLE 2 Tensile Yield Elongation strength strength percentage [MPa] [MPa] [%] Tissue shape Comparative 538 512 15 Surface example1 538 512 15 coarse particles (Commercial 7041) 529 504 14 (Recrystallization), 530 503 16 Internal fibrous 507 485 15 phase 494 476 15 524 499 16 481 464 16 483 466 16 Preferred 425 367 18 Equiaxed grain example1 432 377 19 435 384 20 453 431 17 457 435 17

According to the table 2, it can be seen that the yield strength of the comparative example 1 (commercial 7041) is 450˜550 MPa, and the yield strength of the preferred example 1 is 350˜450 MPa. That is, it can be seen that the yield strength of the preferred example 1 is sufficiently satisfied, even if Cu, a major addition element to increase the strength, was added with a smaller amount than in the comparative example 1. Also, it can be seen that the preferred example 1 has a tissue shape of equiaxed grains, whereas the comparative example 1 has surface coarse particles or an internal fibrous phase. This will be explained in more detail with reference to FIGS. 2A and 2B which will be described later.

FIGS. 2A and 2B are images of tissue shapes according to comparative example 1 and preferred example 1 each having a composition ratio shown in the table 1.

Referring to FIG. 2A, the comparative example 1 has a tissue shape of surface coarse particles or an internal fibrous phase. Thus, the material for appearance of an electronic device, using the comparative example 1, shows streaking due to the tissue shape of FIG. 2A, and has a difficulty in implementing an aesthetic impression of high quality due to the streaking.

Referring to FIG. 2B, the preferred example 1 has a tissue shape of equiaxed grains. More specifically, an average grain size of particles which form equiaxed grains may be 30˜500 μm. The tissue shape of equiaxed grains are more compact than that of coarse particles or an internal fibrous phase. The preferred example 1 having the aforementioned tissue shape of equiaxed grains does not have a particle shape of a metallic tissue, and defects on its surface.

In another preferred embodiment, was prepared a specimen having a composition ratio shown in the following table 3, within the scope of the present invention.

TABLE 3 Weight % Si Fe Cu Mn Mg Zn Cr Ti Zr Al Comparative example 2 0.6~00.9 <0.15 0.5~0.8 0.2~0.5 0.9~1.3 <0.1 <0.1 <0.1 — Bal. Preferred example 2 <0.2 <0.2 <0.1 <0.2 1.5~2.1 5.5~6.5 <0.1 <0.1 — Bal.

In order to compare the characteristics of the comparative example 2 and the preferred example 2 each having composition ratios shown in the table 3, a tensile strength and a yield strength of each of the specimens according to the comparative example 2 and the preferred example 2 were measured by a universal testing machine. Then, result values through the measurement were operated to calculate a mechanical characteristic such as an elongation percentage. And the specimens underwent an anodizing process, and a color and a surface state thereof were shown in the following table 4.

TABLE 4 Comparative Preferred Characteristics example 2 example 2 Mechanical Tensile strength [MPa] 360 453 characteristics Yield strength [MPa] 310 432 Elongation 12.6 17.0 percentage [%] Anodizing Color L* = L* = quality 79.0b* = 2.73 87.7b* = −0.17 (Appearance Streaking Existence Nonexistence characteristics)

According to the table 4, it can be seen that the yield strength of the preferred example 2 is more excellent than that of the comparative example 2, even if Cu, a major addition element to increase the strength, was added with a smaller amount than in the comparative example 2. That is, in the preferred example 2, the mechanical strengths were significantly increased as the amount of Mg and Zn was controlled. Furthermore, it can be seen that the preferred example 2 has a more excellent appearance characteristic having no streaking than the comparative example 2, and has not become yellowish after an anodizing process. The characteristic related to ‘yellowing’ will be explained in more detail in FIG. 3 which will be described later.

FIG. 3 shows images of specimens after an anodizing process, according to comparative example 2 and preferred example 2 each having a composition ratio shown in the table 3.

Referring to FIG. 3, the colors of the specimens after an anodizing process according to comparative example 2 and preferred example 2, can be compared to each other. More specifically, the comparative example 2 becomes yellowish after an anodizing process, thereby having a difficulty in implementing an aesthetic impression of high quality when used as a material for appearance of an electronic device. On the other hand, the preferred example 2 does not become yellowish after an anodizing process, thereby representing a unique color of a dye at the time of applying the dye.

The degree of yellowing may be measured by L*a*b* color system. In the L*a*b* color system, L* is used as an index to indicate a brightness. A black color scarcely having a brightness may have the L* of 0, whereas a white color having a high brightness may have the L* of 100. And a*b* indicates a chromaticity such as a color and a chroma, a* is an index to indicate a red color, and −a* is an index to indicate a green color according to a numerical value. Further, b* is an index to indicate the degree of yellowing, and the degree of yellowing of specimens may be compared to each other through the b* values. More specifically, b* indicates a yellow color, and −b* indicates a blue color. That is, when the colors of the preferred example 2 and the comparative example 2 shown in the table 4 are compared to each other, it can be seen that the preferred example 2 scarcely has a yellow color.

As aforementioned, the aluminum alloy according to the present invention does not become yellowish after an anodizing process. And the aluminum alloy according to the present invention does not have a particle shape of a metallic tissue and defects, on its surface. Thus, the aluminum alloy according to the present invention can represent a unique color of a dye at the time of applying the dye, and can make a dye applied uniformly. Accordingly, when the aluminum alloy according to the present invention is utilized as a case of a mobile terminal, an aesthetic impression can be enhanced.

Further, since the aluminum alloy according to the present invention has the strength high enough to protect inner components of a mobile terminal, it is suitable to be utilized as a case of the mobile terminal.

Hereinafter, a method for preparing an alloy according to the present invention will be explained in brief.

FIG. 4 is a flowchart for preparing an aluminum alloy material for appearance of an electronic device according to the present invention.

Referring to FIG. 4, the aluminum alloy according to the present invention, which has the aforementioned composition ratio, is prepared as a billet through a well-known continuous casting process. Then, the aluminum alloy is made as a product after undergoing a uniform thermal process, an extrusion, a cooling process, a stretching process, and a thermal process, so as to be processed as a material for appearance, such as a cover case, a case frame and a bezel.

In an embodiment, a billet may be prepared by using the aluminum alloy having the aforementioned composition ratio, and then an aluminum alloy material for appearance may be prepared through an extrusion. The preparation of the aluminum alloy material for appearance through an extrusion is a method for obtaining an extruded material having the same shape as a metallic pattern, by injecting a metal into the metallic pattern which has been mechanically processed precisely in correspondence to a required shape. Thus, a material for appearance can be prepared freely without a restriction of design.

Since an extruded shape through the extrusion has a precise dimension (size), time taken to perform a subsequent treatment can be reduced, mechanical characteristics are excellent, and a massive production can be performed. Further, since the production cost is low, the present invention can be utilized in various fields such as a cover case of an electronic device, a case frame, a bezel, a car component, an optical device, and a measuring instrument. The above statements related to the casted shape are merely exemplary, and thus the present invention is not limited to this.

In an embodiment, a billet formed of the aluminum alloy according to the present invention is prepared. Then, a uniform thermal process is performed for 1˜12 hours at a temperature of 440˜550° C., and a hot compression process for the billet is performed at a temperature of 300˜550° C. After the hot compression process, the billet is cooled to a room temperature by a water cooling process or an air cooling process. Then, a thermal treatment is performed for 12˜100 hours at a temperature of 80˜150° C., thereby preparing the aluminum alloy for appearance of an electronic device according to the present invention, as a product.

It will be apparent to those skilled in the art that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof.

Also, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its scope as defined in the appended claims, Therefore, all changes and modifications that fall within the metes and bounds of the claims, or equivalents of such metes and bounds are therefore intended to be embraced by the appended claims. 

1. An aluminum alloy composed of, by weight: 0.2% or less of Si; 0.2% or less of Fe; 0.6% or less of Mn; 1.5˜2.1% of Mg; 5.5˜6.5% of Zn; 0.1% or less of Ti; 0.1% or less of Cr; 0.1% or less of Zr; inevitable impurities; and the balance Al.
 2. The aluminum alloy of claim 1, further comprising 0.1% or less of Cu.
 3. The aluminum alloy of claim 2, wherein the alloy is composed of equiaxed grains.
 4. The aluminum alloy of claim 2, wherein an average aspect ratio of particles of the alloy is 0.6˜1.3.
 5. The aluminum alloy of claim 4, wherein an average grain size of the particles of the alloy is 30˜500 μm.
 6. The aluminum alloy of claim 1, wherein b value is −0.5˜0.5 on 3D coordinates of Lab color system.
 7. The aluminum alloy of claim 1, wherein a ratio of a weight amount of Zn with respect to a weight amount of Mg is 3˜4. 